1. Field of the Invention
Apparatuses and methods consistent with the present general inventive concept relate an image forming apparatus and a belt cleaning unit thereof, and more particularly to an image forming apparatus whose cleaning structure is improved.
2. Description of the Related Art
An electrophotographic type image forming apparatus performs a series of processes including charging, exposing, developing, transferring and fusing to form image on a printing medium, and includes a multi-function printer, a laser printer and others known in the art.
As illustrated in FIGS. 1 and 2, such a conventional electrostatic type image forming apparatus has a photosensitive drum 3 and a transfer belt 11 rotated in a track.
In FIG. 1, the transfer belt 11 is rotated in a track by two rollers, that is, a driving roller 13 and a driven roller 15. In FIG. 2, the transfer belt 11a is rotated in a track by three rollers, that is, a driving roller 13a, a driven roller 15a and an auxiliary driven roller 12. As the transfer belt 11 may be elongated or contracted according to environmental condition such as temperature and humidity, the types of the transfer belt illustrated in FIGS. 1 and 2 are used so that the transfer belt 11 can have its tension of a predetermined range irrespective of the environmental condition. According to the type of the transfer belt illustrated in FIG. 1, an elastic force is applied to the driven roller 15 to be separated from the driving roller 13 in a direction N which is parallel to a line (hereinafter, referred to as a ‘center line’) A connecting rotation centers of the driven roller 15 and the driving roller 13.
Alternatively, according to the type of the transfer belt illustrated in FIG. 2, the elastic force is applied to an additional auxiliary driven roller 12 in a direction P with respect to the center line A in a state of fixing the rotation centers of the driven roller 15a and the driving roller 13a constant, thus maintaining tension of the transfer belt 11.
Also, as illustrated in FIGS. 1 and 2, the conventional image forming apparatus 10(10a) has a belt cleaning unit 16(16a) to remove waste developer remaining on the transfer belt 11(11a). In this case, the belt cleaning unit 16(16a) has a blade 18(18a) and a blade supporting member 17(17a). The blade 18(18a) is made of elastic material and contacts the transfer belt 11(11a) to scrape off the waste developer from the belt 11(11a). Also, the blade supporting member 17(17a) is rotated around a fixed hinge point 19(19a) and supports the blade 18(18a).
However, according to the conventional image forming apparatus 10, as illustrated in FIG. 1, the driven roller 15 slides to approach or depart from the driving roller 13 to maintain the tension of the transfer belt 11, while the position of the blade 18 is fixed by the hinge point 19, thus changing a contact point of the belt 11(11a) that contacts the blade 18 with the transfer belt 11. Accordingly, a contact pressure between the blade 18 and the transfer belt 11 is changed, which can generate poor cleaning and cause damage on the blade 18 and the transfer belt 11 if an excessive contact pressure is applied.
Also, according to the second image forming apparatus 10a, as illustrated in FIG. 2, the contact point between the blade 18a and the transfer belt 11a can be maintained to be stationary. However, as the auxiliary driven roller 12 moves up and down toward the direction P, the transfer belt 11a may slip or move obliquely. Also, an addition of the auxiliary driven roller 12 causes an increase in the cost and a decrease in space efficiency.
Also, as illustrated in FIGS. 1 and 2, even if cleaning of the waste developer is not required, the blade 18(18a) is always in contact with the transfer belt 11(11a). Accordingly, the blade 18(18a) or the transfer belt 11(11a) is worn rapidly and thus decreasing durability.